Project Information

Abstract:

The primary purpose of this project was to demonstrate whether it is possible to operate a subsurface drip irrigation (SDI) system under organic standards and specific processes to stay within the National Organic Plan (NOP) standards. SDI offers many advantages over surface laid drip tape for growing crops but comes with one main disadvantage: keeping the tape emitters clear without using sulphuric acid, the industry norm for cleaning SDI systems. Sulphuric acid is a prohibited substance under NOP. Results of the two year project demonstrated that it is indeed possible to operate SDI under NOP standards, but special precautions need to be taken.

Major lessons learned are: 1) SDI requires no/minimal tillage practices, 2) Tractor equipment equipped with GPS technology is critical, 3) A Zetacore catalytic water treatment system is essential, 4) A robust and well-designed filtration system is required, 5) Continual maintenance of the system is necessary, 6) Flushing the lines with each irrigation event is critical and 7) Periodic flushing of the drip line with hydrogen peroxide is critical.

Introduction

The subsurface drip irrigation system (SDI) began as an idea here in 2007 when Rio Grande Community Farm (RGCF) made a conscious decision to move into organic vegetable production in a much more intentional manner. RGCF is a non-profit farm “working on public land in the public interest.” We farm approximately 50 acres in a variety of crops and are located on a 140 acre plot owned by the City of Albuquerque. We have farmed the land as a non-profit since 1997. With the recession and after a reexamination of our Mission, the RGCF Board decided to focus on growing food crops for our citizens, particularly targeting vegetable crops for our school system, Albuquerque Public Schools (APS). Since 2008 RGCF has had a contract to sell vegetables to APS.

At the same time, the City of Albuquerque applied to utilize an existing well on the property that had not been used for several years. The City had the water rights, but in order to perfect the rights it was required by the State Engineer to install “highest and best use” technology in utilizing the well water. This coincided with our application under the NRCS EQIP program to install a drip irrigation system on 16 acres. We appreciate the strong support given us by Josh Sherman and his staff in the Albuquerque USDA office for the EQIP grant which partially funded the installation of the SDI system. Josh suggested we install “subsurface drip” as it was considered the #1 technology regarding water use efficiency for vegetable crops.

During the installation period from 2008-2010, I had blithely assumed there would be ample information available on the operation of a SDI system under organic certification. This turned out to be far from true – in fact there is almost no information available on organic operation of an SDI system. Realizing that what we would be doing would be of great interest to many farmers in the Southwest and across the nation, we applied for a USDA Conservation Innovation Grant (CIG) and a Western SARE grant. The CIG program in particular requires the integration of two or more existing proven technologies that have been proven effective in agriculture, but whose integration together has not been proven or well-documented. Western SARE targets farmers utilizing innovative technology to meet demonstrated regional challenges. Our use of SDI technology clearly met these criteria. Under the Western SARE grant we have operated under the mentorship and collaboration with the Bernalillo County Extension office which is part of our land grant university, New Mexico State University. Our mentor and Western SARE sponsor, Joran Viers, has been a tireless and always supportive partner in the rollout and implementation of the SDI irrigation system. Joran is the Bernalillo County Extension Director and has been a supporter of organic and sustainable farming for many years. We also appreciate the ongoing support of Norm Vigil and Seth Fiedler in the USDA New Mexico State office for the CIG grant. We could not have completed this project without the expert advice of Seth on navigating the myriad federal forms involved and Norm for ongoing support in the concept of organic SDI.

A brief description of subsurface drip technology

Simply stated, SDI is the use of plastic drip irrigation tape that is semi-permanently buried in the ground. Subsurface drip and above ground drip share many of the same challenges and vary in the overall system components only slightly. Both require pumps to pressurize the system and filters to clean the water. Both require valves, zone stations and pressure regulators to control the areas irrigated. Both involve extensive piping in the form of manifolds, flush valves and main lines to distribute the water. Both involve drip tape with emitters that release the water to the plants. For subsurface drip (SDI), the tape is buried in the ground anywhere from 6”-18” below grade, and the expectation is that it is not removed for several years. Surface tape is often rolled out every year. Occasionally it is re-used, but standard practice is often to throw it away and use new tape every year.

For both surface and subsurface drip tape, a major challenge is to keep the emitters clear and water flowing out of the emitters. There are a number of reasons why emitters get clogged. In addition to the many benefits of burying the tape, the main challenge is how to keep the tape intact and damage free from a variety of four-legged and two-legged creatures. And herein lies one of the major conclusions of our study.

As funny as it may sound, neither Dan our Chief Farmer, nor myself fully understood the implications of subsurface drip. It hit us one day full force after the system was installed and we were planning for crop production. Dan had literally hooked up the five ton double gang heavy discs and was preparing to disc the field. In one of those “ah-ha!” moments Dan and I looked at each other and exclaimed “Holy Cow! We can’t do this anymore!”

Subsurface drip requires you to engage in minimal/no till tillage operations to avoid cutting the lines. Our lines are buried 6” below the surface, and we have had to retool and rethink all our tillage practices. So here is a major conclusion: if you install subsurface drip, you will be engaged in no/minimal till tillage. Both Dan and myself are traditional farmers in that we have used shanks, discs, plows and other implements that greatly disturb the soil. But with the installation of the SDI, we were now instantly no till!

Having realized that we were not only beginning to use new drip technology but also needed to retool all our operations, we went screaming to our USDA partners and Western SARE mentor Joran Viers: “What the heck do we do?!?” Well, we formed the Brain Trust. This is a group of several individuals that have met on a regular basis in 2010/2011 and intermittently since. Their brain power, and more importantly their emotional and psychological support, have been invaluable in overcoming the many challenges of operating an SDI system under organic certification, using no/minimal till methods. Members of the Brain Trust are:

This group met regularly and their feedback and collaborative spirit was truly inspiring. Without their sagacity – and sense of humor – we could not have made the transition to SDI no/minimal till.

A hearty and deep felt thanks also goes out to the following folks for support:

Deb Thrall of the Albert Pierce Foundation
McCune Foundation
Albuquerque Community Foundation
Craig Maple, Brett Baker and Joanie Quinn of the NM Department of Agriculture
Dr. Ron Gooden and Don Bustos on advice regarding no till
The many vendors who donated time, expertise or materials to the project including Dusty Singh of Sierra Irrigation/Barron Supply, Franks Supply, Bern Maier of New Mexico State University, Keden Burk of EuroDrip USA, Mauro Herrera of NM office USDA, Brent McGill of Mueller, Inc.
Parks and Recreation Department and the Open Space Division, City of Albuquerque

We also visited or had discussions with the following farms using SDI:

We are grateful to these farmers for the information they shared and their pioneering spirit. We appreciate Howard Wuertz and son David in particular for the many hours they spent showing us their 5,000 acres in subsurface drip. Howard pioneered this technology in the 1970s and continues to this day to develop implements and processes for SDI and no/minimal tillage. We purchased our first no till implement – a “lister/peeler” from the Wuertz family during our visit in 2009. See Appendix A for information on Howard Wuertz and his farm.

Project Objectives:

To document the procedures, processes and activities involved in operating a subsurface drip irrigation system, including extensive data collection.

Cooperators

Research

The primary challenge in operating a SDI system is to prevent emitter clogging. We have developed several solutions for common causes of emitter plugging:

Emitter clogging due to:
-Sand: Most well water has a high percentage of sand. Design the system to use either a fine mesh prefilter such as the Lakos spinner screen or a centrifugal sand separator.

– Calcium carbonate precipitates: This is the most common cause of emitter clogging and is evidenced by a white “scale” in the lines and emitters. The Zetacore unit has proven effective in eliminating all types of scale. However, the traditional treatment is to lower the ph of the water by using acid to less than 7.0. NOP standards do allow the use of Acetic acid for this purpose. See Attachment P for information on food grade 100% acetic acid.

– Iron and manganese precipitates: Iron and manganese will precipitate out as solids at a wide ph range (ph 4.0-9.5) so acidifying the water has little effect. The Zetacore unit has proven effective in keeping the iron and manganese in solution in the water. We have seen no iron or manganese precipitates in our lines.

– Iron bacteria slime: This has been an issue for us. There are certain strains of bacteria that eat iron and develop long strands of slimy filaments. These form a sort of glue that can clog emitters. The Zetacore does not prevent the bacteria from forming the slime. The most effective prevention of this is use of hydrogen peroxide. Because we have a two chamber concrete box, we are able to add hydrogen peroxide via a dripper system. This is a continuous low dosage feed of hydrogen peroxide that keeps the iron algae at bay. Periodic flushing with hydrogen peroxide also cleans the lines.

– Large particles from surface (ditch) water: Both ditch and well water enter the system through one side of the two chamber box. Water is screened through a fine mesh Lakos brand spinner filter and this screens out large particles. Any remaining particles are screened out through the sand media filters. The sand media filters are set to automatically backflush when they become clogged, but during the growing season we backflush more often than is required, to keep the sand filters clean. Important tip: there is a gate valve that controls the rate of backflush water. Instruction manuals for the sand media filters instruct you to set this valve at the point where the sand media in the tank is raised up during backflush but is not washed out. However, we have set the gate valve to wash out a slight amount of sand with every backflush. This assures complete flushing of the system but does require us to monitor the sand level in the filters. We replace missing sand monthly.

– Fine silt: Neither the Lakos spinner filter nor the sand media filters can screen out the very fine silt that is in the surface (ditch) water. This silt appears as a very fine brownish powder that has the consistency of talcum powder. The silt is fine enough to pass through the emitters but if allowed to build up could cause problems. Flushing for two minutes each time you irrigate eliminates this problem. Also note that one solution to the problem of both fine and large particulate matter is a settling pond. We do not have the space for this, however we have seen applications where surface water is allowed to settle in a large pond and the intake water for the sand media filters is siphoned off the top. This works well but also brings with it the possibility of algae growth in the pond water.

Emitter clogging due to soil ingestion from vacuum pressure: In all drip systems, when the drip lines deflate at the end of an irrigation cycle, a vacuum is created in the lines as the water seeps out the emitters. This vacuum can suck mud back into the emitters. One-way air intake valves at every point are the solution. These should be placed at all high points in the system and be installed on the main line, manifolds and submanifolds. These allow air to come in behind the escaping water, eliminating the suction effect.

Emitter clogging due to growth of algae and bacteria at the emitter zone. Systems that routinely inject fertilizer create nutrient rich zones at the emitters. These zones are not only good for the growing plants but also fungus, algae, bacteria and other microscopic organisms. These organisms create slime that can plug the emitters. To date (three years operation) we have not injected any fertilizers into the system. We have relied on traditional organic methods of fertilizing such as side dressing and foliar feeding. We are however, inching closer to fertigation as we further refine our flushing and maintenance procedures using hydrogen peroxide. Fertigation is one of the main benefits of a drip system, but should be approached with caution.

Before injecting any fertilizer into the system, jar tests should be completed. This involves mixing the fertilizer with both surface water and well water (in separate tests). Besides particulate matter in the fertilizer that can clog emitters, fertilizers can react with minerals in your water, causing unanticipated precipitates. There are also differing opinions on where fertilizers should be injected into the system. Some manufacturers recommend injecting before the sand media filters. This allows the sand media to filter out any reactions but also increases the organic matter in the filters. Others recommend injecting after the filters, but this involves the chance of sending particulate precipitates down the line. We are leaning towards injecting after the sand media filters and after the Zetacore water treatment unit, as the Zetacore minimizes particulate precipitation.

Root intrusion: Root intrusion occurs when very fine roots grow into the emitters, seeking water. Avoid crops such as celery that create very fine roots. Also use an emitter design that is anti-root intrusion. (Check with the tape manufacturer). Also once a crop is growing, maintain adequate watering to prevent roots from searching for water. We have found that our annual high concentration hydrogen peroxide flush flushes out small hair roots. Also cranking up the flush pressure to 30 psi in the drip tape flushes out roots.

Tape damage by gophers: OK, this is a big one, and we have not found any real solution, other than repairing lines. Gophers burrow from point A to point B and chew anything in their way. They do not chew the tape to get water. We have tried a variety of traps, prevention (castor beans, vibrating fans) and scare tactics – nothing works. We cannot use toxic chemicals or poisons under NOP, so we just live with them. We are now trying a new approach – installing several owl boxes in the hope of creating habitat for gopher predators. But in the meantime, grab the ole repair bucket…

Incorrect tape injection: The process of injecting the tape at the initial installation is critical. Use experienced personnel and high quality equipment. Injection should not be a place to cut corners. You definitely need to inject with GPS technology to assure accurate placement. Also note that all buried drip tape should be laid with the emitters face up. During injection, it is easy for the tape to become twisted and a section is injected emitter down.

Proper system design, flow rate, tape size, emitter spacing, emitter rating, tape thickness, run distance, tape operating pressure, depth of placement, slope of land, manifold length, zone size – all these are factors in assuring a working system and must be calculated ahead of time. Work with a design professional to run the numbers to assure success. Often the tape distributor can provide this service. There are three main tape suppliers – EuroDrip, Netafim and T-Tape. Research each one and make an informed decision.

Seed germination: This is a major issue and one that needs to be carefully considered. What crops will you be growing? What is your soil type? Are you hand or tractor scale? We intentionally placed our tape rather shallow (6″-8″ below grade) to facilitate the germination of small cover crop seed such as clover and sorghum/sudan. We also went with a shallower injection because our soil tends to be sandy. On sandy soil, water leaches down faster than it wicks up, so the distance the water must travel at germination can’t be too far. On higher clay soils that support upwards wicking of water, a deeper tape injection is possible. At initial germination of a cover crop seed, we generally let the system run 12-24 hours. The soil is thoroughly soaked at this point. Most of our vegetable crops are transplants, so the issue of germination is not as critical. We also supplement water when transplanting starts (we fill the transplant hole with water from a tank).

Insect damage to tape: This has not been an issue for us – usually affects surface tape.

Tape damage by tillage practices: This has been an issue – we have chopped through, dug up, severed, made holes in, squashed, twisted, hit with shovels and in a dozen more creative ways managed to damage the tape. Lesson learned: outfit your tractors with GPS technology and perform the majority of your no/minimal tillage operations with GPS. Otherwise just get used to fixing leaks.

Research results and discussion:

Without exception the single most important innovation in our system has been the use of the Zetacore catalytic water treatment unit. This technology has been around a long time, mostly in golf course systems, and is relatively unknown to agricultural users. However, the effects on minerals in water is dramatic, and we clearly demonstrated this in the past three years. We saw zero clogging in the emitters over three years. This combined with our use of hydrogen peroxide and other procedures has demonstrated that this technology can work. Recommended action? Every farmer who has any type of irrigation system should install a Zetacore unit to treat the water.

Reactions from Producers

One of the most common reactions is: “it looks awfully expensive”. This is a valid point but when compared to the long term benefits, investment in this technology will pay off.

Producers have been uniformly impressed with the Zetacore, particularly when I show the mineral buildup on untreated water versus treated water.

Educational & Outreach Activities

Participation Summary

Education/outreach description:

We are just now organizing our outreach efforts, now that the Monograph is completed. We will post the information on our website, distribute to the USDA and other outreach activities. We are scheduled to discuss the project at the 2013 New Mexico Organic Conference scheduled for February, 2013.

Project Outcomes

Project outcomes:

The Top Thirteen Tips for operating a SDI system under organic certification:

1. Installing SDI requires you to practice no/minimal tillage techniques. Be prepared to retool and rethink how you do all your tillage.

2. Have GPS on your tractors. Although we injected the tape in the ground using GPS technology, our tractors are not outfitted with GPS. We thought we could easily track the location of the drip tape by eye, using the mounded up rows as a guide. This has proven harder than we expected, particularly when the zones have thick cover crops.

4. Regularly use hydrogen peroxide to clean your drip and system lines.

5. Do not use the system to inject fertilizers. Use alternate organic methods for fertilization.

6. Flush the lines at the ends with every watering event.

7. In the height of the season, when iron algae is prevalent, pour hydrogen peroxide into your water containment box, or use a dripper.

8. Install a prefilter or sand extractor before the sand media filters.

9. Use 15-17 mil tape so you can flush periodically at high pressures.

10. Write a detailed Maintenance Schedule and stick to it – regular maintenance is key.

11. Use acetic acid to lower the ph of the water.

12. Routinely test your water and soil so you know what you are dealing with.

13. Backflush at a high flow rate, washing out a small amount of sand each time. Keep an eye on sand levels (in the sand media filters) and replace as necessary.

We have operated our 16 acre subsurface drip system for three growing seasons under NOP organic standards and have had great success. We have had no plugging of the emitters to date and no major problems with the system. The greater challenge has been to modify our tillage practices to not damage the buried drip tape. We are now an “organic no-till” operation, and this has already resulted in dramatically improved soil. We are currently working with the USDA to measure the effects of no-till and to date results are encouraging. Our “active carbon” component in the soil has doubled over the three years we have been doing this.

The biggest challenge is not having GPS technology on our tractors and the consequent repairs we must make when we damage the drip lines. But we are learning…

For further information contact Minor Morgan at (505) 379-1640 or info@riograndefarm.org.

Recommendations:

Potential Contributions

Of 21 types of irrigation methods the USDA tracks, SDI is the top of the list for water efficiency. With changing world climate patterns and deepening drought in the Southwest, there is no question that water efficiency in irrigation must become paramount. During the three years we have been working on this project, we have had over 20 producers/growers come visit the farm, ask questions and consider how our experience affects them. One of the most important conclusions is that the techniques we use because of NOP Standards can be adopted by traditional growers. Harsh chemicals are not essential to operating a SDI system. This is the single most important conclusion of the project. We have already seen an improvement in our soil quality since adopting SDI and no/till practices.

Future Recommendations

One exciting aspect of having such a nimble and highly controllable SDI system is the potential for matching the water needs of a crop with its growth cycle. We have not taken advantage of this, but this represents an important area of research. This would involve installing moisture sensors and doing the research on each crop to determine how much water is needed at what phase of growth and then using the system to deliver that water.

Another area of research is fertigation. As outlined in our main report, we do not practice fertigation at this point but feel the system is capable of this. However, exactly what fertilizers, their proportions and injection protocols would all need to be researched.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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